Optical apparatus with lens position detection and control

ABSTRACT

An optical apparatus includes a first motor arranged to vary a magnifying power, a second motor arranged to make compensation when the first lens moves and also to adjust focus, a first motor arranged to move the first lens in the direction of an optical axis, a stepping motor being arranged as the first motor, a second motor arranged to move the second lens in the direction of the optical axis, a detecting part arranged to detect the position of the first lens on the basis of the number of driving pulse steps of the first motor, a memory circuit arranged to store information on adequate second lens moving positions in relation to specific moving positions of the first lens, and a control circuit arranged to control a driving action of the second motor on the basis of information on the position of the first lens detected by the detecting part and the information on the adequate moving position of the second lens.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an optical apparatus to control an inner focustype lens system.

2. Description of the Related Art

It is known that an inner focus type lens system includes afocusing-compensator lens which is arranged in rear of a variator lenson its optical axis to serve both as a compensator lens and a focusinglens. Therefore, the position of the focusing-compensator lens at whichan in-focus state is obtainable on an image pickup plane varies with adistance to a picture-taken object even if the focal length of theoptical system is kept constant.

When the object distance is changed at each of different focal lengths,the position of the focusing-compensator lens for obtaining an in-focusstate on the image pickup plane varies as indicated by pointscontinuously plotted in FIG. 2. A zooming operation can be carried outwithout any blur by selecting a specific locus from among a plurality ofloci shown in FIG. 2 according to the object distance and by moving,during zooming, the focusing-compensator lens according to the specificlocus.

Meanwhile, in the case of a front-lens focus type lens system, acompensator lens is arranged independently of a variator lens. Further,the variator lens and the compensator lens are connected to each otherby a mechanical cam ring. Therefore, if, for example, a manual zoomingoperation ring is provided on the cam ring for manually varying thefocal length, the cam ring follows the operation ring to enable thevariator and compensator lenses to move along the cam groove of the camring, no matter how fast the operation ring is moved. Therefore, no blurwill be caused by the movement of the operation ring as long as thefocusing lens is in an in-focus position.

With respect to the control over the inner focus type lens system whichhas the characteristic mentioned above, it is generally practiced tohave information on the plurality of loci shown in FIG. 2 stored in asuitable form in a lens control microcomputer, to select one of the lociaccording to the position of the focusing-compensator lens and that ofthe variator lens, and to perform zooming while tracing the locusselected.

According to the conventional practice, however, a moving speed of thefocusing-compensator lens and a point to which the focusing-compensatorlens is to be moved are determined according to the position of thevariator lens. Therefore, the conventional practice has the followingdrawbacks:

(1) If the position of the variator lens is not accurately detectedwithin a given allowable error range, it is hardly possible to correctlyread out the locus data corresponding to the actual position of thevariator lens. The inaccurate detection of the position of the variatorlens degrades the accuracy of focusing to be carried on during theprocess of zooming. Therefore, it is necessary to use a highly accuratedetector for the detection of the position of the variator lens.However, the use of an accurate detector results in a cost increase.

As apparent from FIG. 2, the locus data gradually approaches to a shapeperpendicular to the abscissa axis near a telephoto end position of thevariator lens. It is known that this tendency becomes more salientaccordingly as the magnifying rate of the variator lens is higher. Inorder to accurately store the locus data for positions near thetelephoto end, therefore, the position detecting accuracy for thevariator lens must be increased for a greater magnifying power of thelens system.

(2) Since the focusing-compensator lens must be smoothly moved accordingto the movement of the variator lens, the moving speed of the variatorlens must be kept constant. In cases where a DC motor is used fordriving the variator lens like the conventional arrangement, it isnecessary for this purpose to apply servo-control to the driving actionof the DC motor or to finely adjust the movement of thefocusing-compensator lens by relatively accurately detecting thefluctuations in the moving speed of the variator lens during zooming.

The necessity of the servo-control and the detection of fluctuations inthe moving speed not only imposes restrictions on design but alsodirectly causes increases in the number of parts and in the load ofmicrocomputer programs.

SUMMARY OF THE INVENTION

One aspect of this invention resides in the provision of an opticalapparatus which is of the kind using and controlling an inner focus typelens system, wherein a stepping motor which performs a stepping actionis used as a drive source for a variator lens, the position of thevariator lens is detected from the number of driving steps of the motor,a plurality of specific positions of the variator lens preset forrespective focal lengths of the lens system are detected, and themovement of a focusing-compensator lens for the plurality of specificpositions is controlled on the basis of information obtained from memorymeans, so that the focusing-compensator lens can be accurately moved.

The above and other aspects and features of the invention will becomeapparent from the following detailed description of an embodimentthereof taken in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the arrangement of an optical apparatus asan embodiment of this invention.

FIG. 2 is a graph showing a relationship between the position of avariator lens and that of a focusing-compensator lens necessary formaintaining an in-focus state at each of various focal lengths.

FIG. 3 is a graph showing the locus tracing method in the embodiment.

FIG. 4 is a flow chart showing the operation of a microcomputer shown inFIG. 1.

FIG. 5 is a graph showing a method for moving the focusing-compensatorlens following the movement of the variator lens.

FIG. 6 is a graph showing another method for moving thefocusing-compensator lens following the movement of the variator lens.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 shows the arrangement of an optical apparatus as an embodiment ofthis invention. Referring to FIG. 1, an inner focus type lens system iscomposed of elements 101, 102, 103, 104 and 105. These elements includea fixed front lens group 101, a second lens group 102 for varying amagnifying power, a diaphragm 103, a third lens group 104 which isfixed, and a fourth lens group 105 which has both a focusing functionand a function of making compensation when the magnifying power varies.Switches 107 and 110 are provided respectively for detecting that thesecond lens group 102 and the fourth lens group 105 are in theirrespective reference positions. In the case of FIG. 1, these switches107 and 110 are respectively disposed at these lens groups together withphoto-sensors 108 and 111. The switch 107 is secured to the second lensgroup 102 and the switch 110 is secured to the fourth lens group 105.The switches 107 and 110 are thus arranged to move in parallel to theoptical axis as the lens groups 102 and 105 move in parallel to theoptical axis, and to selectively act to block or not to block the lightoutputs of the photosensors 108 and 111 with the middle parts of themovable range of these lens groups taken the respective boundaries. Thelight detecting part of each of the photo-sensors 108 and 111 isarranged to output a signal of "1" or a signal or "0" according towhether the light output is blocked or not blocked. A point at which thesignal output of each of the light detecting parts changes is consideredto be the reference position. Therefore, whether the lens groups 102 and105 are in the above-stated reference positions or not can be determinedon the basis of these points. The apparatus is provided with an imagesensor 106, an encoder 109 for detecting the aperture position of thediaphragm 103, an amplifier or an impedance converter 112, a known AGC(automatic gain control circuit) 113, a filter 114 for extracting only ahigh-frequency component of a video signal, a signal processing circuit115 which is arranged to process the video signal for AF (automaticfocusing), a microcomputer 116 for driving control over the lens system,an amplifier 117 for amplifying the output signal of the encoder 109, asignal conversion circuit 118 arranged to convert the output signal ofthe amplifier 117 into a signal readable by the microcomputer 116, acontrol circuit 119 arranged to detect the level of the output signal ofthe AGC 113 and to adjust the aperture position of the diaphragm 103 insuch a way as to keep the level constant, an amplifier 120 foramplifying the output of the control circuit 119, a driver 121 fordriving the diaphragm 103, drivers 126 and 122 for applying drivingenergy to stepping motors 127 and 123 according to instructions givenfrom the microcomputer 116 for driving the second and fourth lens groups102 and 105, the stepping motors 123 and 127, output gear shafts 124 and129 which are connected directly to the stepping motors 123 and 127,racks 125 and 128 arranged for the output gear shafts 124 and 129respectively to move the lens groups 105 and 102 which are secured tothem by moving in parallel to the optical axis when the output gearshafts 124 and 129 are rotated, a pull-up resistor group 130, a powersupply 131, switches 132 and 133 for moving the second lens group 102toward a wide-angle end and toward a telephoto end, respectively, andswitches 134 and 135 for moving the fourth lens group 105 respectivelytoward an infinity distance position and toward a nearest distanceposition.

With the inner focus type lens system arranged as shown in FIG. 1, whena magnifying power varying action is performed by moving the second lensgroup 102, the in-focus positions of the fourth lens group 105 obtainedat various focal lengths give the loci as shown in FIG. 2. In otherwords, in order that a power varying action is to be performed whilekeeping an in-focus state, information about the loci shown in FIG. 2 isstored in some suitable form (either in the form of loci or in the formof functions with the lens positions used as variables) in a memory(ROM) provided within the microcomputer 116, the locus information thusstored is read out according to the position or a moving speed of thevariator lens (the second lens group 102), and the focusing-compensatorlens (the fourth lens group 105) is moved in accordance with the locusinformation read out.

FIG. 3 shows, by way of example, a method for tracing the above-statedloci in accordance with this invention. Referring to FIG. 3, a series ofpoints a0, a1, a2, --all and another series of points b0, b1, b2, --b11obtained respectively at a plurality of specific positions z0, z1, z2,--z11 of the variator lens 102 indicate the representative loci storedwithin the microcomputer 116. Further, a series of points c0, c1, c2,--c11 show a locus obtained by computation on the basis of theabove-stated two loci. The computing operation is performed inaccordance with the following formula:

    c(n+1)=|c(n)-a(n)|/|b(n)-a(n)|*.vertline.b(n+1)-a(n+1)|+a(n+1)                           (1)

According to the formula (1), in a case where the focusing-compensatorlens is located at the point c0 in FIG. 3, for example, a ratio in whicha line segment b0--a0 is internally divided by the point c0 is obtained,and then, a point at which another line segment b1--a1 is internallydivided in accordance with the ratio thus obtained is considered to bethe point c1.

This embodiment is arranged on the premise that the formula (1) is to beused. Information on the loci thus must be stored in such a manner thatall the loci shown in FIG. 2 are obtainable by using the formula (1).

FIG. 4 is a flow chart showing a flow of a program provided within themicrocomputer 116 for the purpose of tracing a locus obtained in theabove-stated manner. Referring to FIG. 4, the program is as follows:

When the execution of the program begins at a step 401, the position ofthe variator lens (the second lens group 102) and that of thefocusing-compensator lens (the fourth lens group 105) are detectedrespectively at steps 402 and 403. In the case of this embodiment, thestepping motors 127 and 123 are employed as actuators for these lenses.Therefore, the positions of these lenses 102 and 105 are detectablesolely by means of the lens controlling microcomputer 116. Morespecifically, the stepping pulses required for moving these lenses 102and 105 are generated at the microcomputer 116. When the pulses aregenerated at the microcomputer 116, a counter disposed within themicrocomputer 116 is reset at the reference position mentioned in theforegoing. Therefore, the positions of these lenses can be detected fromthe increment and decrement of the count value of the counter. Further,information about the plurality of specific positions z0 to z11 ofcourse can be detected also from the count value of the counter.

At a step 404, after the absolute positions in the direction of theoptical axis of the lenses 102 and 105 have been detected in the mannermentioned above, a check is made to find if a computing operation can becarried out according to the formula (1). The computing operationaccording to the formula (1) is possible only when the variator lens(the second lens group 102) is located in one of the specific positionsz0, z1, z2, --shown in FIG. 3. Therefore, at the step 404, the check ismade to find if the variator lens is in one of these specific positions.If so, the flow of the program comes to a step 405. At the step 405, twostored values of the points a0 and b0 located above and below the pointc0 at which the focusing-compensator lens (the fourth lens group 105) islocated are searched for from the memory. At a step 406, the value ofthe point cl is computed according to the formula (1). At a step 407,the movement locus of the focusing-compensating lens (the fourth lensgroup 105) resulting from variations of the magnifying power isdetermined according to the computed value of the point c1. Further,this locus computation can be serially carried out for segments betweenthe points c0 and c1, c1 and c2, c3 and c4, c4 and c5, --. Therefore, alocus ranging from the telephoto end position over to the wide-angle endposition can be obtained at once even when the variator lens is in thetelephoto end position by repeating the computing operation at the steps406 and 407. It is also possible to compute one segment of the locus ata time by each round of the flow of the program.

If the data computation is found to be impossible at the step 404, theflow comes to a step 408 by, for example, using a previously computedlocus without newly performing the locus computation. At the step 408, acheck is made to find if either the switch 132 or the switch 133 hasbeen pushed. If not, the movement of the variator lens (the second lensgroup 102) is caused to stop at a step 409. At a step 410, an automaticfocusing or a manual focusing associated with the operating state of theswitch 134 or 135 is effected.

If either of the switches 132 and 133 is found to be pushed at the step408, the flow comes to a step 411 to move the variator lens 102according to the state of the switch 132 or 133. Zooming can beaccomplished without any blur, correctly tracing the locus, by movingthe focusing-compensator lens 105 (the fourth lens group) from a pointc0 to a point cl when the variator lens 102 comes from its position z0to another position z1. Therefore, it is necessary to predict the timeof arrival of the variator lens at the position z1. The use of thestepping motor 127 as an actuator for the variator lens 102 enables thelens controlling microcomputer 116 to accurately predict (or adjust) thearrival time and to move the variator lens 102 accurately to the desiredposition. Therefore, at a step 412, the time of arrival of the variatorlens 102 at the position z1 is confirmed. At a step 413, by using amethod which will be described by way of example later herein, controlinformation about the moving speed and the moving time for thefocusing-compensator lens 105 is determined. At a step 414, thefocusing-compensator lens 105 is moved according to control informationdetermined at the step 413.

A method for determining the control information for thefocusing-compensator lens 105 at the step 413 is described by way ofexample as follows: FIGS. 5 and 6 show methods for moving thefocusing-compensator lens 105 when the variator lens 102 is moved fromits position z0 to its position z1 with the points c0 and cl determined.

In the case of FIG. 5, a speed at which the focusing-compensator lens105 is to be moved from the point c0 to the point cl is computed fromthe time required for moving the variator lens 102 from the position z0to the position z1. The focusing-compensator lens 105 is then moved atthe computed speed following the movement of the variator lens 102.

According to a method shown in FIG. 6, the focusing-variator lens 105 ismoved at a high speed from the point c0 to the point cl at a time afterarrival of the variator lens 102 at the position z1.

Further, as shown in FIG. 3, the plurality of specific positions z0, z1,z2, z3, --z11 of the variator lens 102 which are set for controlling themovement of the focusing-compensator lens 105 are not evenly spaced. Thespacing distance varies according to the focal length, because themovement locus of the focusing-compensator lens 105, as shown in FIGS. 2and 3, has a steeper inclination on the telephoto side than other parts.It is thus deemed to be necessary to have more accurate control on thetelephoto side. The movement of the focusing-compensator lens 105 can beaccurately controlled by arranging the spacing distance between thespecific positions of the variator lens to be shorter for the focallength area where the movement locus of the focusing-compensator lens105 has a steeper inclination.

As described in the foregoing, the embodiment is arranged to use astepping motor as an actuator for the variator lens of an inner focustype lens system and to obtain a plurality of specific positions of thevariator lens. This arrangement enables the embodiment to highlyaccurately control the position and the moving speed of the variatorlens. Spacing distances among the specific positions are differentiatedone from another according to the focal length. Therefore, the movementlocus set for the focusing-compensator lens can be accurately tracedduring zooming even if the magnifying power varying rate of zooming ishigh. The arrangement of the embodiment thus enhances the accuracy offocusing to be carried on during the zooming operation.

What is claimed is:
 1. An optical apparatus comprising:a) a first lensarranged to perform a magnifying power varying action; b) a second lensarranged to both make compensation at the time of a movement of saidfirst lens and adjust a focus of said optical apparatus; c) a firstmotor for moving said first lens in the direction of an optical axis ofsaid optical apparatus, said first motor being a stepping motor; d) asecond motor for moving said second lens in the direction of the opticalaxis; e) detecting means for detecting a position of said first lens,said detecting means being arranged to detect the position of said firstlens on the basis of the number of driving pulse steps of said firstmotor; f) a memory circuit storing each adequate moving position of saidsecond lens based on each moving position of said first lens, saidmemory circuit being arranged to store said each adequate movingposition of said second lens corresponding to each of a plurality ofspecific positions of said first lens to be detected by said detectingmeans; and g) a control circuit arranged to control a driving action ofsaid second motor on the basis of information on the position of saidfirst lens detected by said detecting means and information on said eachadequate moving position of said second lens stored in said memorycircuit.
 2. An apparatus according to claim 1, wherein said detectingmeans is arranged to detect said plurality of specific positions andalso positions between said plurality of specific positions.
 3. Anapparatus according to claim 1, wherein a stepping motor is employed assaid second motor.
 4. An apparatus according to claim 1, wherein saidcontrol circuit is arranged to control the driving action of said secondmotor by reading out from said memory circuit the information on saidadequate moving position of said second lens which is taken when saidfirst lens is in a certain specific position of said plurality ofspecific positions.
 5. An apparatus according to claim 4, wherein saidcontrol circuit is arranged to obtain, by computation, a driving speedof said second motor by obtaining time at which said first lens reachessaid certain specific position.
 6. An apparatus according to claim 4,wherein said control circuit is arranged to cause said second motor tobegin a driving action thereof after said first lens reaches saidcertain specific position.
 7. An apparatus according to claim 3, furthercomprising second detecting means for detecting a position of saidsecond lens on the basis of the number driving pulse steps of saidsecond motor.
 8. An apparatus according to claim 7, wherein said controlcircuit is arranged to control the driving action of said second motorfurther on the basis of information on the position of said second lensdetected by said second detecting means.
 9. An apparatus according toclaim 8, wherein said control circuit is arranged to control the drivingaction of said second motor by reading out from said memory circuit theinformation on said adequate moving position of said second lens whichis taken when said first lens is in a certain specific position of saidplurality of specific positions.
 10. An apparatus according to claim 9,wherein said control circuit is arranged to obtain, by computation, adriving speed of said second motor by obtaining time at which said firstlens reaches said certain specific position.
 11. An apparatus accordingto claim 9, wherein said control circuit is arranged to cause saidsecond motor to begin a driving action thereof after said first lensreaches said certain specific position.
 12. An optical apparatuscomprising:a) a first lens arranged to perform a magnifying powervarying action; b) a second lens arranged to both make compensation atthe time of a movement of said first lens and adjust a focus of saidoptical apparatus; c) a first motor for moving said first lens in thedirection of an optical axis of said optical apparatus, said first motorbeing a stepping motor; d) a second motor for moving said second lens inthe direction of the optical axis; e) detecting means for detecting aposition of said first lens, said detecting means being arranged todetect the position of said first lens on the basis of the number ofdriving pulse steps of said first motor; f) a memory circuit storingeach adequate moving position of said second lens based on each movingposition of said first lens, said memory circuit being arranged to storesaid each adequate position of said second lens corresponding to each ofa plurality of specific positions of said first lens to be detected bysaid detecting means, said plurality of specific positions beingdifferently spaced according to focal lengths; and g) a control circuitarranged to control a driving action of said second motor on the basisof information on the position of said first lens detected by saiddetecting means and information on said each adequate moving position ofsaid second lens stored in said memory circuit.
 13. An apparatusaccording to claim 12, wherein said detecting means is arranged todetect said plurality of specific positions and also positions betweensaid plurality of specific positions.
 14. An apparatus according toclaim 12, wherein a stepping motor is employed as said second motor. 15.An apparatus according to claim 13, wherein said plurality of specificpositions are arranged to be spaced narrower for telephoto positionsthan middle positions.
 16. An apparatus according to claim 15, whereinsaid control circuit is arranged to control the driving action of saidsecond motor by reading out from said memory circuit the information onsaid adequate moving position of said second lens which is taken whensaid first lens is in a certain specific position of said plurality ofspecific positions.
 17. An apparatus according to claim 16, wherein saidcontrol circuit is arranged to obtain, by computation, a driving speedof said second motor by obtaining time at which said first lens reachessaid certain specific position.
 18. An apparatus according to claim 16,wherein said control circuit is arranged to cause said second motor tobegin a driving action thereof after said first lens reaches saidcertain specific position.
 19. An apparatus according to claim 14,further comprising second detecting means for detecting a position ofsaid second lens on the basis of the number driving pulse steps of saidsecond motor.
 20. An apparatus according to claim 19, wherein saidcontrol circuit is arranged to control the driving action of said secondmotor further on the basis of information on the position of said secondlens detected by said second detecting means.
 21. An apparatus accordingto claim 20, wherein said control circuit is arranged to control thedriving action of said second motor by reading out from said memorycircuit the information on said adequate moving position of said secondlens which is taken when said first lens is in a certain specificposition of said plurality of specific positions.
 22. An apparatusaccording to claim 21, wherein said control circuit is arranged toobtain, by computation, a driving speed of said second motor byobtaining time at which said first lens reaches said certain specificposition.
 23. An apparatus according to claim 21, wherein said controlcircuit is arranged to cause said second motor to begin a driving actionthereof after said first lens reaches said certain specific position.